1. Field of the Invention
The present invention relates to an electric wheel drive which is applied to, for example, a dump truck for use in a mine, a wheel loader, a scraper, a dozer, a towing tractor and the like.
2. Related Art Statement
Electric wheel drives are disclosed in U.S. Pat. Nos. 4,330,045; 3,686,978; 3,387,502 and 3,035,652.
Conventional electric wheel drives are divided into two types on the basis of the position of a reduction gear as shown in FIGS. 20 and 21. Both types employ an air-cooled motor and a dry-type brake.
More particularly, the conventional electric wheel drive includes one type in which a reduction gear is disposed at the inner side of a vehicle body with respect to a motor and a brake device which are disposed at the outer side of the body than the motor as shown in FIG. 20. The other type includes a first-stage planetary reduction gear disposed at the outer side of the body with the motor and a second-stage star-type reduction gear disposed outside of the planetary reduction gear. The first-stage planetary reduction gear of FIG. 21 is disposed inside of a hub bearing disposed outside of the wheel body.
However, such conventional electric wheel drives have problems as described below. Description is now made to the problems in detail with reference to the drawings.
Referring to FIG. 20 showing the former type drive in section, the former type includes first-stage and second-stage reduction gears 61 and 62 disposed at the inner side the vehicle body 51 relative to the motor 53, the motor 53 being disposed in an axle case 52 mounted on the body 51 and the brake device being disposed at the other side of the motor 53 near the outside H of the body 51. With such a construction type, however, it is necessary to remove tires 63 from a hub wheel case 57 and remove the axle case 52 from the body 51 upon maintenance of the reduction gears 61 and 62. Particularly, in a large-sized vehicle, much labor is required due to the weight of the tire 63 and the axle case 52. In the drive of this type, the power of the motor 53 is transmitted to the tires 63 through the first and second stage reduction gears 61 and 62. However, since the first stage reduction gear 61 is a conventional external-type gear and the second stage reduction gear is a conventional internal-type gear, it is limited in a confined space to largely reduce the high rotational power of the motor 53 and transmit the power of low speed and high torque to the tires 63. Further, cooling air for cooling the motor 53 of FIG. 20 is generally taken in from the side G of the body and is led through a gap 56 between a gear case 55 and the axle case 52 to the motor 53. Then, the cooling air passes through the brake device 54 and is exhausted outside of the axle case 52 from an outlet 58. In this case, however, since the passage of the cooling air is prevented by the gear case 55 and the cooling air takes a long way around the gear case, the cooling air suffers loss and is warmed by the gear case 55. Accordingly, it is not preferable for cooling the motor 53.
In FIG. 20, the motor 53 is disposed in the axle case 52 mounted to the body 51 and the rotary power of the motor 53 is reduced through the first and second stage reduction gears 61 and 62 and transmitted to the tires 63. Since the first stage reduction gear 61 is a conventional external type gear and the second stage reduction gear is a conventional internal type gear, it is limited in a confined space to largely reduce the rotary power of the motor 53 and transmit the power of low speed and high torque to the tires 63.
On the other hand, referring to FIG. 21 showing the latter type drive in section, the motor 73 is disposed at the innermost side of the axle case 72 mounted on the vehicle body 71. The first-stage planetary reduction gear 81 is disposed at the outer-side N of the vehicle body 71 with respect to the motor 73 and the second-stage star-type reduction gear 82 is disposed outside of the first-stage planetary reduction gear 81 so that the power of the motor 73 is transmitted to the tires 83. The brake device 74 is mounted to the outside of an external cover 75 of the axle case. In the drive of this type, cooling air for cooling the motor 73 is taken in the motor 73 from an inlet 76 and is exhausted outside of the motor 73 from an outlet 77 of the motor 73. The cooling air is then exhausted outside of the vehicle body 71 through a gap 78 between the axle case 72 and the motor 73. However, air warmed by the motor 73 passes outside of the motor 73 and hence it is not desirable with respect to cooling efficiency.
While the drive shown in FIG. 21 includes the motor 73 disposed at the innermost side of the axle case 72 mounted to the vehicle body 71, the first-stage planetary reduction gear 81 disposed at the outer-side N of the vehicle body with respect to the motor 73 and inside of the hub bearing and the second-stage star-type reduction gear 82 disposed outside of the first-stage planetary reduction gear whereby the rotary power of the motor 73 is transmitted to the tires 83. However, in this drive, the reduction ratio of the first-stage planetary reduction gear 81 is determined by a diameter of the hub bearing so that it is difficult to obtain a large reduction ratio.